The first thing to ask is if you are pay monthly or PAYG? This thread can then be moved to the correct board where you will receive an good response for your tariff.

To roam in the USA or Canada you will need a quad band phone, if you are using an iphone this should support the frequencies used in the USA and Canada.

If you are on a pay monthly red entertainment plan, you should have Global Roaming Plus added to your account and this will mean you will be able to use your phone without incurring the pay monthly daily roam further charge of £6.00 per day.